Turbomachines include gas turbine engines such as auxiliary power units, propulsive gas turbine engines deployed onboard aircraft and other vehicles, turboshaft engines utilized for industrial power generation, and non-gas turbine engines, such as turbochargers. Generally, a turbomachine includes a compressor section, a combustion section, and a turbine section. During operation, air flows through the stages of the turbomachine as follows. The compressor section draws ambient air into the inlet of the turbomachine, compresses the inlet air with one or more compressors, and supplies the compressed inlet air to the combustion section. The combustion section also receives fuel via a fuel injection assembly, mixes the fuel with the compressed air, ignites the mixture, and supplies the high energy hot combustion gases to the turbine section. The turbine section drives one or more turbines, including a shaft that may be used to drive the compressor and other components. The flowpath is defined by air moving through the stages in the turbomachine, inclusive of the inlet air, compressed inlet air and hot combustion gases.
Turbomachines often employ centrifugal compressors as a means to compress air prior to delivery into the engine's combustion chamber. The rotating element of the centrifugal compressor, commonly referred to as an impeller, is typically surrounded by a generally conical or bell-shaped shroud, which helps guide air in the flowpath from the forward section (commonly referred to as the “inducer” section) to the aft section of the impeller (commonly referred to as the “exducer” section).
Some conventional impeller designs, commonly referred to as ported shroud impellers, boost performance by extracting air from the flowpath through various methods. Air flow may be extracted in either of two directions, depending upon the operational conditions of the impeller. Conventional ported shroud impeller designs then either reintroduce the extracted air into the flowpath (typically at the impeller inlet) or dump the extracted air overboard (with an associated penalty to the engine cycle). Specifically, when the impeller is operating near the choke side of its operating characteristic, the conventional ported shroud impeller “in-flows” or reintroduces extracted air into the flow path (that is, draws air into the impeller through at least one opening) to increase the choke side range of the impeller operating characteristic; and, when the impeller is operating near the stall side of its operating characteristic, the conventional impeller shroud outflows (that is, bleeds or extracts air from the impeller through at least one opening) to increase the stall side range of the impeller operating characteristic. While conventional ported shroud impellers of the type described above can increase impeller performance within limits, further improvements in efficiency are desirable.
Accordingly, an improvement in efficiency that simplifies design complexity, parts count, and weight, is desirable. The desirable improvement in impeller efficiency is not reliant upon an extraction of air from the flowpath and is achieved without a corresponding decrease in flow capacity, pressure ratio, or surge margin. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.